Electroplating uses electrical current to reduce cations of a desired material from a solution and coat a conductive object, the work piece, with a thin layer of the material, such as a metal. In a typical electroplating cell, the part to be plated is the cathode and the anode is made of the metal to be plated on the part. Both components are immersed in an electrolyte containing one or more dissolved metal salts as well as other ions that permit the flow of electricity through the electrolyte. Metal atoms of the anode are oxidized to ions, allowing them to dissolve in the electrolyte. In this manner, the ions in the electrolyte bath are continuously replenished by the anode. At the cathode, the dissolved metal ions in the electrolyte solution are reduced at the surface of the cathode, such that they “plate out” onto the cathode.
The above described method of plating uses a “consumable” anode, that is, during plating the anode is dissolved into the electrolyte and eventually is consumed and must be replaced in order to electroplate further. As the anode is consumed, it undergoes shape change during plating. This shape change can have detrimental effects on plating uniformity because the change in shape of the anode creates a change in the plating conditions. For example, the electric field shape and density between the work piece and the anode changes during plating due to the change in distance between the work piece and the anode due to the anode's consumption. In certain plating applications, for example electroplating a metal onto a semiconductor wafer, it is important to have highly uniform plating onto the semiconductor wafer. When plating layers that are very thin, on the order of angstroms or microns thick, and where uniformity is critical, even small changes in the anode's shape can create non-uniformities in the plated metal.